Improved cryogenic connection

ABSTRACT

In a cryogenic connection wherein tubular conductors insulated by a vacuum and carrying a cryogenic fluid, provides a fluid connection between the vacuum surrounding the current conducting tubular conductors with the annular cavity also subjected to vacuum pressure between inner and outer enclosures providing thermal insulation to the cryogenic connection. The coupling of connection elements is effected in a sequential conductor laying process, utilizing rectilinear sections of 20-metre enclosures and of semirigid conductor tubes of similar length.

United States Patent [1 1 Moisson-Franckhauser et a1,

451 Apr. 30, 1974 IMPROVED CRYOGENIC CONNECTION [75] Inventors: FrancoisMoisson-Franckhauser, Sur

Orge; Marcel Aupoix, Paris, both of France [73] Assignee: CompagnieGenerale DElectricite,

Paris, France [22] Filed: Mar. 23, 1973 [21] Appl. No.: 344,406

[30] Foreign Application Priority Data Mar. 31, 1972 France 72.11553[52] US. Cl. 174/15 C, 174/22 C, 174/27, 174/28, l74/D1G. 6 [51] Int. ClH0lv 11/00 [58] Field of Search 174/D1G. 6, 15 C, 16 B, 174/27, 28, 22C, 23; 335/216 [5 6] References Cited UNITED STATES PATENTS 650,9876/1900 Ostergren...-; 174/15 C X 3,343,035 9/1967 'Garwin 174/15 C UX3,431,347 3/1969 Kafl a et a1 174/15 C 3,522,361 7/1970 Kafka 174/15 C3,686,422 8/1972 D0056 174/15 C 3,693,648 9/1972 Sassin 174/15 C X3,694,914 10/1972 Aupoix et a1. 174/15 C X 3,726,985 4/1973 Aupoix etal. 174/15 C 3,723,634 3/1973 Aupoix et al. 174/15 C PrimaryExaminerBemard A. Gilheany Assistant Examiner-A. T. Grimley Attorney,Agent, or Firm-Sughrue, Rothwell, Minn, Zinn & Macpeak [5 7] ABSTRACT Ina cryogenic connection wherein tubular conductors insulated by a vacuumand carrying a cryogenic fluid, provides a fluid connection between thevacuum surrounding the current conducting tubular conductors with theannular cavity also subjected to vacuum pressure between inner and outerenclosures providing thermal insulation to the cryogenic connection. Thecoupling of connection elements is effected in a sequential conductorlaying process, utilizing rectilinear sections of 20metre enclosures andof semirigid conductor tubes of similar length.

9 Claims, 4 Drawing Figures PATENTEWR 30 ran sun-1r a or 3 IMPROVEDCRYOGENIC CONNECTION BACKGROUND OF THE INVENTION 1. Field Of TheInvention The present invention concerns an electric cryogenicconnection comprising cables insulated by a vacuum, provided with adevice for subjecting the annular space which ensures the electricalinsulation of the phase conducting tubes with the cryogenic connectionbeing used for conveying high voltage electrical alternating current.

2. Description Of The Prior Art One known type of cryogenic connectioncapable of conveying high voltage electrical alternating currentcomprises an inner enclosure, coaxial pairs of tubular conductors insidethe inner enclosure with the number of pairs of conductors dependingupon the number of phases of alternating current conveyed. A pair ofcoaxial conductors consists of an inner tubular conductor conveying acryogenic fluid and an outer tubular conductor. The inner enclosureitself contains a cryogenic fluid which immerses the outer conductor.Vacuum is created on the one hand in the space between the inner andouter conductors, and on the other hand, in the space between the innerand out enclosures which surround the coaxial conductors. In general,the vacuum is created independently in these two spaces which does notpermit the effective vacuum pumping of the spaced formed between theinner and outer conductors, whose residual'pressure, when cryogenicpumping 'is carried out, is due to the accumulation of helium comingvery small leakages in the tubular conductors, that is, the accumulationof the cryogenic fluid flowing through the inner tubular conductor.

The aim of the present invention is to overcome these disadvantages.

SUMMARY OF THE INVENTION The present invention has for its object theformation of a cryogenic electrical connection comprising cablesinsulated by a vacuum, wherein the connection comprises an innerenclosure, at least one pair of tubular coaxial conductors within theinner enclosure and constituted by anouter tubular conductor and aninner tubular conductor, means for providing cryogenic fluid flow in theinner conductor, an outer enclosure surrounding the inner enclosure andthe space between the inner and outer enclosures being subjected to avacuum pressure with the cryogenic connection being characterized byproviding fluid communication between the space formed between the innerand outer conductors and the space formed between the inner and outerenclosures and therefore subjects the space between the inner and outerconductors to vacuum pressure, effecting fluid communication betweenthese spaces and the space between the outer conductor and the innerenclosure.

An example of a cryogenic connection according to the invention ensuringthe placement of the space in which a vacuum is maintained into fluidcommunication, will be described with reference to three diagrammaticfigures. With respect to these figures, like numerals designate likecomponents. Several devices for establishing fluid communication betweenthose spaces subjected to vacuum pressure are provided at intervalswhich are, to great advantage, spaced by 10 to 100 meters.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an exploded, perspectiveview of a cryogenic connection provided with the arrangement forestablishing fluid communication according to the in- DESCRIPTION OF THEPREFERRED EMBODIMENT The device shown in FIG. 1 is an example of anembodiment of the invention, makes it possible to connect two sectionssuch as 10 and 20 of a cryogenic connection within an outer enclosure 1.In each section, there are provided three pairs of coaxial tubularconductors which lie inside inner enclosure 5. Each pair of coaxialtubular conductors comprise a tubular inner conductor 2, suitable forconveying a cryogenic fluid, and a tubular outer conductor 3concentrically surrounding the tubular inner conductor 2 and spacedtherefrom. Vacuum is created in the space 4 between the inner and outerconductors and between the outer enclosure 1 and the inner enclosure 5while a cryogenic fluid immerses outer conductor 3 and flows between theinside of the inner enclosure 1 and outer conductors 3. The figures showthree pairs of tubular coaxial conductors, by way of an example of theembodiments of a cryogenie connection which is able to convey a threephase alternating current.

The inner conductor 2 constitutes the phase conductor, whereas the outerconductor 3 constitutes the neutral conductor. The vaccum created in thespace 6 which separates the inner enclosure 5 from the outer enclosure 1provides a good thermal insulation for the cryogenic connection. Withrespect to the coaxial tubular conductors, the inner and outerconductors 2 and 3 respectively are separated by means of insulatingspacers such as spacers 19. The insulating spacers 19 are formed by thethermal assembly of two sectors and their function is to contain theelectro-dynamic efforts exerted between the inner and outer conductors,and contribute to the electrical insulation by the vacuum existingbetween the inner and outer conductors, the limiting of the thermallosses between the outgoing helium circuit within the inner conductorsand the return helium limit to the inside of the inner enclosure 5,while allowing for limited vacuum pumping impedance and enabling'theinner and outer conductor tubes to fit together and the sliding of thegroup of inner and outer conductor tubes. These spacers are installedremote from the site of assembly and that is at their point ofmanufacture before the inner and outer tubes, for example, 20-metertubes are fitted together. The pairs of coaxial conductors 2 arecorrugated tubes made of copper covered with a niobium deposit which ispolished, then covered, for example, with polytetrafluorethylene. Theaim of this manufacturing technique is to protect the niobium layermechanically when assembling and to protect the niobium layer at thelevel of the insulating spacers 19 when subjected to vibrationassociated with electrodynamic forces and to improve the dielectricstrength and to reduce the ionizing currents taking into account theangle of losses of the polytetrafluorethylene which is less than that ofother dielectrics at a temperature of 5 Kelvin.

The outer conductors such as 3 are free of corrugations, that is, theyare cylindrical over a short portion of their length, that is,approximately one meter. They have in their corrugated portions adiameter whose bulk is slightly less than that of the their cylindricalportions. They may be fitted without difficulty over a portion of theirlength into cylindrical tubes 110 which form a part of the assembly 100,according to the invention, the tubes 110 having a diameter slightlygreater than the diameter of the conductors 3 at their cylindricalportion. The cylindrical portions of the tubes 3 lie within assembly 100and are now shown in FIG. 1. The assembly 100 comprises on the one handtwo identical flanges 119 and 120 which at their peripheries areprovided with rims 121 and 122 respectively welded to the ends of innerenclosure 5 for sections and 20. On the other hand, at least three tubessuch as 101, 102 and 103, have ends welded respectively to the flanges119 and 120 to permit fluid communication between sections 10 and 20 ofthe connectors. Furthermore, cylindrical tubes such as 110, 111 and 112are provided at spaced circumferential positions, the number of tubesbeing equal to the number of pairs of conductors, with respective tubesreceiving the pairs of coaxial conductors. The outgoing flow ofcryogenic fluid occurs within the inner conductor tubes, while thereturn flow of cryogenic fluid occurs within the space between the outerconductors 3 and the inner enclosure 5.

At a position defined by the assembly 100, helium flow on the inside asdefined by flanges 119 and 120, is limited to the set of tubes 101, 102,103, 110, 111, and 112, and limited on the outside by the space betweenthe outer conductors 3 and the inner enclosure 5 with the outer faces offlanges 119 and 120 being subjected to helium pressure. The heliumcircuit is therefore as follows: three outgoing tubes consisting of thethree inner conductor tubes 2 between the cooling means and a connectionto the helium return circuit, a return tube by the space between theouter conductors 3 and the inner enclosure 5, in turn connected to thecooling means (not shown). The choice of material is particularlyimportant in that type of device because of the electrical andmechanical stresses. By way of example, this choice is made as follows:the end flanges 119 and 120 and the cryogenic flow tubes 101, 102 and103 are made of an iron and nickel alloy containing 30 to 45 percentnickel; that alloy being, for example, of a type known in France by thetrade name INVAR. The tubes such as 110, 111, 112 surrounding each pairof coaxial conductors have their ends 14 and 15 made of INVAR, whereastheir intermediate portion 12 may be made of copper. That structure maybe formed, for example, by means of an electroforming method.

The tubes such as 101, 102, 103 made on INVAR which ensures that thegreater part of the cryogenic fluid flow is liquid helium flow, forexample, also allow the transfer of longitudinal mechanical tensilestresses existing in sections 10 and 20 of the connectors to be made ofINVAR whose rectilinear shape gives rise to no reduction in its lengthwhen cooling is effected.

The present invention is directed to the communication of spaces 4 and 6which may be subjected to common vacuum. In this regard, by reference toFIG. 3, an orifice of oblong shape is formed in the central cop'- perportions within each of the tubes 110, 111 and 112, the axis of thatorifice being parallel to that of the tubes and situated on anaccessible face of that tube which forms a part of the connection. Anorifice 91 whose shape is oblong, having dimensions smaller that that orequal to that of orifice 90 is formed in the outer conductor for each ofthe tubes 110, 111 and 112, these orifices being in each case the othersextension. A local deformation 92 of the tubes 110, 111 and 112 puts therim of the orifices 90 in contact with the outer conductor tubes 3 and aweld 17 is provided between the copper tubes around the perimeter of theorifice 90.

Since the axis of the orifice is of oblong shape and is parallel to thatof the conductor, the currentlines in the conductors are not greatlydisturbed in the vicinity of that orifice and do not give rise to anyappreciable electrical losses at that point. Moreover, the helium flowin the annular space between the outer conductor 3 and the tube 110 isnot greatly disturbed, subsequent to the direction of the axis of theorifice, the stabilization of the supraconductor of the conductor tube 3is ensured, while the heat exchange between the conductor 3 and theflowing helium remains satisfactory throughout virtually the wholeperimeter of the tube 3. The arrangement for communicating spaces 4 and6 is best seen in FIG. 3 which is a transverse cross-sectional view ofassembly seen in FIG. 1. FIG. 3 effectively shows the weld at 17, foreach pair of coaxial conductors, with this weld connecting together theedges of the orifices 90 which are oblong shaped formed in the outerconductor 3 and in the duct 112 and thus enabling the space 4 betweenthe inner conductor 2 and outher conductor 3 to communicate with thespace 6 between the inner enclosure 5 and outer enclosure 1. It is quiteobvious that there is a weld such as 17 for each pair of coaxialconductors. The vacuum may thus be common to spaces 4 and 6 and a singlepumping means (not shown) and coupled to connection via tube 16 is allthat is necessary to provide the desired vacuum pressure. The structurehas, however, the advantage of insuring without discontinuity, thecooling of the outer conductors of each pair of coaxial conductors.Indeed, the cryogenic fluid which flows in the inner enclosure andpasses through tubes 101, 102 and 103 and also flows within tubes 110,111, and 112, round the outer conductor 3. That figure also shows theintermediate portion of copper and an end portion 15 made of IN- VAR, ofthe tube 112. When laying, the three pairs of coaxial conductors 2, 3,are inserted in the three tubes 110, 111, 112, made of INVAR and copper,and pass through the assembly 100 defined by flanges 119 and 120. One ofthe flanges 119 made of INVAR has its rim welded to the end of the innerenclosure 5 which is made of INVAR and contains the pairs of conductors.In the space between flanges 119 and 120, an orifice having an oblongshape is then formed on each of the outer conductors and on each of thetubes 110, 111 and 112, and the welding of the edges of the two orificesthus formed is effected thereon, the edges of these orifices being madeof copper. This method therefore enables the spaces under vacuum to bein fluid communication with each other, while the conductors remain incontact with the helium without discontinuity at the achieved in termsof the described embodiments of the invention is effected as follows:the assembly 100, comprising six tubes 101, 102, 103, 110, 111, 112 andflanges 119, 120, is produced at the factory by welding the tubes to theflanges on the accessible faces of the latter. The adjacent 20 metersections of pairs of coaxial tubular conductors 2 and 3 are welded tothe pairs of conductors previously installed, then put together in arectilinear configuration. A tubular element of the inner enclosure 5 interms of section or section is installed, then welded to the elements ofthe connection previously installed. For ection 10, the inner enclosure5 surrounds the three pairs of conductors 2, 3, these conductorsextending past the free end of section 10 by a length greater than 10meters. The device or assembly formed by tubes 101, 102, 103,110, 111,112 and flanges 119 and 120 is installed by inserting the free ends ofthe coaxial condcutors and sliding them over 10 to 20 meters untilflange 119 comes into contact with the end of the inner enclosure 5forming section 10. This enables the welding of the rim of the flange119 and the inner enclosure 5 for section 10. The conductors 2, 3 have acorrugated free. portion 10 to 20 meters long extending past theconnection point defined by the flange with the ends of these conductorspossibly being set apart from each other, thus enabling circumferentialwelding of the pairs of conductors to a further section of 20 meterconductors. These later conductors 3 are then put together in arectilinear configuration. A second section 20 constituting a further 20meter section of the connection is then installed by connecting theinner enclosure 5 of that section to flange 120. This is achieved bywelding the rims or peripheries of flange 120 and inner enclosure 5 ofsection 20 together since they are both made of INVAR. lnner enclosure 5of section 20 surrounds the pairs of conductors over a portion of theirlength. The following stage of assembly is then effected by joining inalternative fashion, 20 meter enclosure elements to 20 meter conductorelements, the respective connections being staggered with respect toeach other. Lastly, the orifices of an oblong shape are subsequentlyformed in the outer conductors such as 3 and the edge-of these orificesis welded to the edge of orifices formedin tubes 110,111, 112, FIG. 2,this being done before the installing of the outer enclosure 5 of theconnection and possibly before installing of a thermal screen.

The assembling method which has just been described is compatible withthe minimizing of the diameter of the enclosures, by means of thestaggering of the positions at which the connections of the conductorsare formed and of the positions at which the connections of theenclosures are formed. That minimizing of the diameter of the innerenclosure 5 remains unchanged at the point of connection between parts,this being made possible by the ease of access, in three directions,spaced circumferentially apart, for form ing oblong orifices and weldsat that point, when the tubes are put together. This is made easier, duealso to the possibility of opening the end of the conductors which aresemi-rigid, a judicious choice of their structure enabling electricalconnections to be formed before regrouping these conductors.

Connections for dividing the vacuum applied to the cryogenic electricalconnection into sections (not shown) are arranged, for example, every400 meters. Their mechanical function consists in ensuring the fixing ofthe coaxial conductors of the inner enclosure 5 enabling the connectionbetween 400 meter connection sections forming an angle between them.This fixing is necessary subsequent to efforts generated by cooling andpossibly by the existence of declivities. The function of theseconnections with respect to the pumping is to enable the creation of avacuum which is not simultaneous in the 400 meter sections, during theinstalling of the connections, to limit the extent of the zones affectedby leakages, to enable increased pumping at that point in the connectionand detecting of leakages as well as their repair.

The connection between the inner and outer conductors at that point iseffected by means of insulating cross-pieces. These cross-piecescomprise a voltage distributor of the capacitative type formed bydivided conductors embedded, for example, in a phenolic resin; theinsulating cross-pieces being semi-fluid-tight, that is, capable ofholding a primary vacuum when one of the faces is subjected toatmospheric pressure. That characteristic therefore remains compatiblewith their vacuum dividing function.

It is quite obvious that in the structure which has just been described,the means used may be replaced by equivalent means, ensuring the sametechnical functions and that the materials used may be replaced bymaterials having the same mechanical and electrical properties withoutgoing beyond the scope of the invention.

What is claimed is:

1. In a cryogenic connection of the type comprising:

an outer enclosure,

an inner enclosure within said outer enclosure and spaced therefrom,

means for subjecting the space between said outer enclosure and saidinner enclosure to a vacuum,

means for providing a cryogenic fluid flow in said inner enclosure,

at least one pair of tubular coaxial conductors inside said innerenclosure and sealed therefrom, said pair of coaxial conductors beingconstituted by an outer tubular conductor and an inner tubularconductor,

means for providing a cryogenic fluid flow in said inner tubularconductor, and means for subjecting the space between said inner andouter tubular conductors to a vacuum, the improvement comprising:

means for providing communication between the space formed between saidinner conductor and said outer conductor and the space formed betweensaid inner enclosure and said outer enclosure without communicating withthe space formed between said outer conductor and said inner enclosure.

2. The cryogenic connection according to claim 1, wherein said commonmeans for communicating the space between said inner conductor and saidouter conductor and the space between said inner enclosure and saidouter enclosure, on the one hand comprises a first orifice formed in thewall of said outer conductor and on the other hand a second orificeformed in a tubular wall surrounding said outer conductor and forming atight continuation of said inner enclosure, the edges of these twoorifices being connected to each other in a fluid tight manner overtheir complete length.

3. The cryogenic connection according to claim 2, wherein: said firstand second orificies have an oblong shape whose greatest dimensionextends in the longitudinal direction of the conductors.

4. The cryogenic connection according to claim 2, wherein said innerenclosure comprises two sections separated by an assembly, said assemblycomprising: two flanges whose peripheries are sealed respectively to theend of said sections of said inner enclosure and defining a fluid tightchamber therebetween, at least one tube extending in a fluid tightmanner between said flanges for permitting the flow of cryogenic fluidbetween sections of said inner enclosure, said tube connecting orificiesformed within said flanges and tubes surrounding each of said outerconductors and forming a cryogenic flow path about said outer conductorbetween sections of said inner enclosure, and wherein said secondorifice is formed in the tubes surrounding said outer conductor in eachinstance, adjacent to said first orifice with the edges of the first andsecond orifices being in contact with each other by bringing the wallsof the outer conductor and the tube surrounding said outer conductortogether and being sealably joined together by means of a weld.

5. The cryogenic connection according to claim 4, wherein: said firstand second orifices have an oblong shape whose greatest dimensionextends in the longitudinal direction of the conductors.

6. The cryogenic connection according to claim 4,

wherein: said flange, said inner enclosure, said flow tube and at leastthe ends of each tube surrounding said outer conductor are made of aniron and nickel alloy containing 30 to 45 percent nickel.

7. The cryogenic connection according to claim 6, wherein: said firstand second orifices have an oblong shape whose greatest dimensionextends in the longitudinal direction of the conductors.

8. The cryogenic connection according to claim 6, wherein theintermediate portion of each tube surrounding each outer conductor ismade of one material from the group consisting of aluminum and copper.

9. The cryogenic connection according to claim 8,

wherein: said first and second orifices have an oblong shape whosegreatest dimension extends in the longitudinal direction of theconductors.

1. In a cryogenic connection of the type comprising: an outer enclosure,an inner enclosure within said outer enclosure and spaced therefrom,means for subjecting the space between said outer enclosure and saidinner enclosure to a vacuum, means for providing a cryogenic fluid flowin said inner enclosure, at least one pair of tubular coaxial conductorsinside said inner enclosure and sealed therefrom, said pair of coaxialconductors being constituted by an outer tubular conductor and an innertubular conductor, means for providing a cryogenic fluid flow in saidinner tubular conductor, and means for subjecting the space between saidinner and outer tubular conductors to a vacuum, the improvementcomprising: means for providing communication between the space formedbetween said inner conductor and said outer conductor and the spaceformed between said inner enclosure and said outer enclosure withoutcommunicating with the space formed between said outer conductor andsaid inner enclosure.
 2. The cryogenic connection according to claim 1,wherein said common means for communicating the space between said innerconductor and said outer conductor and the space between said innerenclosure and said outer enclosure, on the one hand comprises a firstorifice formed in the wall of said outer conductor and on the other handa second orifice formed in a tubular wall surrounding said outerconductor and forming a tight continuation of said inner enclosure, theedges of these two orifices being connected to each other in a fluidtight manner over their complete length.
 3. The cryogenic connectionaccording to claim 2, wherein: said first and second orificies have anoblong shape whose greatest dimension extends in the longitudinaldirection of the conductors.
 4. The cryogenic connection according toclaim 2, wherein said inner enclosure comprises two sections separatedby an assembly, said assembly comprising: two flanges whose peripheriesare sealed respectively to the end of said sections of said innerenclosure and defining a fluid tight chamber therebetween, at least onetube extending in a fluid tight manner between said flanges forpermitting the flow of cryogenic fluid between sections of said innerenclosure, said tube connecting orificies formed within said flanges andtubes surrounding each of said outer conductors and forming a cryogenicflow path about said outer conductor between sections of said innerenclosure, and wherein said second orifice is formed in the tubessurrounding said outer conductor in each instance, adjacent to saidfirst orifice with the edges of the first and second orifices being incontact with each other by bringing the walls of the outer conductor andthe tube surrounding said outer conductor together and being sealablyjoined together by means of a weld.
 5. The cryogenic connectionaccording to claim 4, wherein: said first and second orifices have anoblong shape whose greatest dimension extends in the longitudinaldirection of the conductors.
 6. The cryogenic connection according toclaim 4, wherein: said flange, said inner enclosure, said flow tube andat least the ends of each tube surrounding said outer conductor are madeof an iron and nickel alloy containing 30 to 45 perceNt nickel.
 7. Thecryogenic connection according to claim 6, wherein: said first andsecond orifices have an oblong shape whose greatest dimension extends inthe longitudinal direction of the conductors.
 8. The cryogenicconnection according to claim 6, wherein the intermediate portion ofeach tube surrounding each outer conductor is made of one material fromthe group consisting of aluminum and copper.
 9. The cryogenic connectionaccording to claim 8, wherein: said first and second orifices have anoblong shape whose greatest dimension extends in the longitudinaldirection of the conductors.